The invention relates to an air nozzle for a jet dryer for the drying of moving material webs of textiles or the like, constructed as a slot nozzle with a nozzle slot extending transverse to the moving material web and having an elongated nozzle lip which, together with the material web moving substantially parallel alongside it, forms over a considerable length the boundary of the channel for the drying air.
An air nozzle of this type for example is known from published examined German patent application 21 56 100. In such prior art air nozzles the air exits from the nozzle slot along a curved surface utilizing the Coanda effect. Downstream of the curved surface the air stream enters a channel bounded on one side by the elongated nozzle lip and on the other side by the moving material web.
For optimum utilization of the drying air, the flow channel, and hence the elongated nozzle lip, heretofore had to be made relatively long with high air velocity and this could result in an undesired fluttering of the material web. The cause of this fluttering lies in pressure variations in the channel flow due to friction with the flow channel walls. These pressure variations result in a pulsating air stream and hence in a fluttering of the material web. Heretofore such fluttering could be avoided or minimized only by increasing the tension of the material web, which, however, is neither desirable nor possible with all materials.